ensure timeline view correctly updates on fade insert/delete

Differential Revision: https://phabricator.kde.org/D18324

Fix copy-pasting between different tracks

See merge request kde/kdenlive!13

BUG: 403242

Change icon if track effects, and make it enable/disable effects

Differential Revision: https://phabricator.kde.org/D18193

BUG: 387503

glwidget refactoring

See merge request kde/kdenlive!11

Fix pasting enlarged image/color/title clips

See merge request kde/kdenlive!12

Make gl client sync function pointer a member variable. In case there is some per-context aspect.

Not a true refactor as one instance of emit gpuNotSupported() did not reset the glslManager. I think this was not intentional tho.

This issue was identified using valgrind. Output:

==200828== Mismatched free() / delete / delete []
==200828==    at 0x4C2E668: free (in
/nix/store/270csszcn55xv52pjmvgr6cgy5grc8y5-valgrind-3.14.0/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==200828==    by 0xAFCBFD0: mlt_profile_close (in
/nix/store/l1dy6sf0sf6j7r7m45sg0xa8i8fxw4zq-mlt-6.13.0/lib/libmlt.so.6.13.0)
==200828==    by 0x7E52F8: GLWidget::~GLWidget() (glwidget.cpp:173)

CCBUG: 401639

Differential revision: https://phabricator.kde.org/D18169

Fixes #15

Fixes #14